ASTM_D_2238_-_92_2012e1.pdf

Designation:D223892(Reapproved 2012)1Standard Test Methods forAbsorbance of Polyethylene Due to Methyl Groups1at 1378cm1This standard is issued under the fixed designation D2238;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1NOTEReapproved with editorial changes in December 2012.1.Scope1.1 These test methods cover measurement by infraredabsorption spectrophotometry of the 1378.4-cm1(7.255-m)band in polyethylene due to methyl groups.(1,2,3-6)2Twotest methods are covered:1.1.1 Test Method A uses compensation with a standardsample film or wedge of known methyl content.1.1.2 Test Method B uses compensation with a wedge ofpolymethylene or a polyethylene of known low methyl content.1.2 These test methods are applicable to polyethylenes ofTypes I(density 910 to 925 kg/m3),II(density 926 to 940),andIII(density 941 to 965).NOTE1For determination of density,see Specifications D1248.NOTE2In cases of Type III polyethylene with densities greater than0.950 g/cm3,different results are obtained with the two test methods.1.3 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific hazardsstatements are given in Section 7.NOTE3There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:3D618 Practice for Conditioning Plastics for TestingD1248 Specification for Polyethylene Plastics ExtrusionMaterials for Wire and CableD1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD1898 Practice for Sampling of Plastics(Withdrawn 1998)4E131 Terminology Relating to Molecular SpectroscopyE168 Practices for General Techniques of Infrared Quanti-tative AnalysisE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsIEEE/ASTM SI-10 Standard for Use of the InternationalSystem of Units(SI):The Modern Metric System3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 absorbancethe logarithm to the base 10 of thereciprocal of the internal transmittance:A 5 LOG101/T!5 2LOG10T(1)3.2 Units,symbols,and abbreviations used in this testmethod appear in Terminology E131 or Practice IEEE/ASTMSI-10.4.Significance and Use4.1 When interpreted with the aid of appropriate calibrationdata,either test method can be used to compare the total methylcontents of polyethylenes made by similar processes.Suchinformation can be interpreted in terms of specific alkyl groupswith the aid of data on infrared absorption at certain otherwavelengths(7).NOTE4The bias of determination of the concentration of total alkylgroups depends on knowing the concentrations of methyl and ethylbranches present,since these branches have anomalously high absorptivi-ties per group at 1378 cm1(7.25 m).4.2 Knowledge of total methyl groups in polyethylene,when combined with data on molecular weight and on reactiveend groups such as vinyl,can lead to assignment of end-groupstructures and can shed light upon polymerization mechanisms.1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.70 on AnalyticalMethods(Section D20.70.08).Current edition approved Dec.1,2012.Published December 2012.Originallyapproved in 1964.Last previous edition approved in 2004 as D2238-92(2004).DOI:10.1520/D2238-92R12E01.2The boldface numbers in parentheses refer to the list of references at the end ofthese test methods.3For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.3 Data on total methyl groups in polyethylene can becorrelated qualitatively with certain polymer properties such asmelting point,density,stiffness,and other mechanical proper-ties that are closely dependent on the degree of crystallinity ofthe polymer.4.4 These test methods are especially suitable for research.They have not been tested for use in manufacturing control.5.Interferences5.1 Compensation minimizes interference from methylenegroup absorption bands at 1368 cm1(7.31 m)and 1352 cm1(7.39 m)with the 1378-cm1(7.255 m)methyl deformationband.5.2 In Test Method A residual absorption is often present at1352 cm1after compensation,